Plone-testing

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- Fixed AttributeError when importing ``plone.testing.z2`` if ``zope.testbrowser`` 4.x is used but not ``zope.app.testing``.
[icemac]

- Broke dependency on `unittest2` for Python 2.7+ as all features of `unittest2` are integrated in `unittest` there.
[icemac]

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- Fix z2.txt doctest for FTP_SERVER.
[timo]

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- Read 'FTPSERVER_HOST' and 'FTPSERVER_PORT' from the environment variables if possible.
This allows us to run tests in parallel on CI servers.
[timo]

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- Replace deprecated Zope2VocabularyRegistry import.
[timo]

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- Factor test request creation out of addRequestContainer into makeTestRequest.
[davisagli]

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- Fix quoting of urls by the testbrowser.
[do3cc]